Aiming to achive the high RF performace AlGaN/GaN HEMT by suppress current collapse and decresing the parasitlic parameters,high density SiN film was deposited by using ICP-CVD on the surface of AlGaN/GaN epi wafer before fabrication of device.The GaN HEMT device was fabricated by removing PECVD passivation around the gate based the etch stop layer of high density SiN.A 6fingers × 50μm GaN HEMT device was fabricated.The device shows a maximum drain current of 900 rnA/mm and a maximum transconductance of 380 mS/mm,a current gain of cut-off frequency(fT)of 45GHz at a gate bias of-1.5V and a drain bias of 20V.The device shows a power density of 4.7W/mm,a power-added efficiency(PAE)of 44.6%and a associated power gain of 8.5dB by Load-pull measurement.A 34-36GHz GaN MMIC was fabricated,which exhibbits a output Power saturation about 41.5dBm,a power-added efficiency(PAE)of 20%and a gain of 15.5dB.